1. Technical Field
The invention relates to a medical or dental handpiece with a tool for the processing of body tissue or of a substitute material by machining.
2. Background Information
In WO 96/14024 a tool is described having an abrasive processing section which is effective laterally and frontally and which is suitable, with an oscillating drive in the sense of a vibration which is transmitted to the tool by a dental handpiece, for preparing a lateral cavity in a tooth. The magnitude of the amplitudes of the oscillating movements is relatively small in the sense of a vibration, with the frequency preferably lying in the ultrasonic range. With this known design the processing section is a processing head which is thickened with respect to the tool shank and which has a cross-sectional shape converging towards its free end. On the side located opposite the lateral processing section the tool has a smooth face. By this means the known tool is suitable for working a cavity in the approximal region of a tooth. In the course of this working procedure the processing section is preferably lowered from the occlusal region towards the cervical region. In this connection the cavity may have already been worked beforehand by means of a rotary tool or it may also be prepared with the processing section without preliminary work. In this connection the adjacent tooth remains unimpaired, since the smooth face located opposite the processing section does not damage the adjacent tooth. The abrasiveness of the effective working faces of the processing section is created by means of a studding of juxtaposed small grains of hard material, preferably of diamond. In functional operation the small hard grains prove to be a plurality of cutting edges, the working faces that are present in each case being effective over substantially their entire area.
The tool according to WO 96/14024 has working faces directed transverse to one another--for example, at least one working face extending in its longitudinal direction and one front face extending transverse thereto--and by reason of a drive having three-dimensional amplitudes it is adapted not only to process surfaces, as is conventional in the case of files, but also to work holes or cavities, in particular blind holes.
The amplitudes of the oscillating movements of the processing section in functional operation may be executed by three-dimensional, circular or elliptical movements in the sense of a vibration. In order to avoid jamming in the course of extracting the tool from the cavity, the processing section has a cross-sectional shape that is convergent towards its free end.
In addition, files for the surface treatment of teeth by machining have become known that have an abrasive working face on a lateral face of a file blade extending along a tool shank. These known files are adapted for an oscillating movement of considerable amplitude length, for example several millimetres, the movement being directed in the longitudinal direction of the shank. These known files are not suitable to prepare a cavity on a tooth, specifically they are not suitable in particular for such a cavity that takes the form of a blind hole. This is predetermined by the fact that the known file does not have a working face extending transverse to the longitudinal direction of the shank and in addition an associated drive device is not adapted for drive movements directed transverse to the longitudinal direction of the shank. These known files are mainly used for the processing of surplus materials by machining and for processing of the surface, specifically also in the approximal tooth region, for which purpose they are suitable by virtue of their design comprising a thin file blade.
In practice, operations to process body tissue or corresponding substitute materials are necessary in various working positions of the tool in confined spatial conditions, as is the case for example in the oral cavity of a patient. For this reason special requirements exist with regard to being able to position the tool in different positions.
To this end it has already been proposed to integrate an adjusting device within a handpiece for holding a tool so that the tool with its holder is capable of being adjusted and positioned in different rotary positions with respect to the handpiece. However, in many cases this adjustability is not sufficient to obtain a favourable working position for the tool. In addition it is difficult and costly to integrate such an adjusting device into the handpiece, since for the purpose of avoiding visual impairments in the course of handling the handpiece the space available in the end region of the handpiece is limited.